/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformString.h
Returns the required buffer length for the [Src, Src+SrcSize) string when converted to the DestChar encoding. The Src range should contain a null terminator if a null terminator is required in the output.
The number of DestChar elements that Src will be converted into.
template<typename DestEncoding, typename SourceEncoding> static int32 ConvertedLength ( const SourceEncoding * Src, int32 SrcSize )